Combine test-bt and test-bt-debug into a single default.release

collection, utilising the new --debug-server option for the debug
run to ensure the correct binaries are used.

Remove test-bt-*fast, they are unused.

mysql-test/collections/default.release

+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=debug      --vardir=var-debug                       --skip-ndbcluster --skip-rpl --report-features --debug-server
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=normal     --vardir=var-normal                      --skip-ndbcluster --report-features
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=ps         --vardir=var-ps                          --skip-ndbcluster --ps-protocol
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=funcs1+ps  --vardir=var-funcs_1_ps --suite=funcs_1  --ps-protocol
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=funcs2     --vardir=var-funcs2     --suite=funcs_2
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=partitions --vardir=var-parts      --suite=parts
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=stress     --vardir=var-stress     --suite=stress
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=jp         --vardir=var-jp         --suite=jp
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=embedded   --vardir=var-embedded                    --embedded-server --skip-rpl --skip-ndbcluster
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=nist       --vardir=var-nist       --suite=nist
+perl mysql-test-run.pl --force --timer --parallel=auto --experimental=collections/default.experimental --comment=nist+ps    --vardir=var-nist_ps    --suite=nist     --ps-protocol

mysql-test/collections/test-bt

-perl mysql-test-run.pl --force --timer --parallel=auto --comment=normal  --skip-ndbcluster --report-features --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=ps --skip-ndbcluster --ps-protocol --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=funcs1+ps  --suite=funcs_1 --ps-protocol --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=funcs2     --suite=funcs_2 --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=partitions --suite=parts   --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=stress     --suite=stress  --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=jp         --suite=jp      --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=embedded  --embedded-server --skip-rpl --skip-ndbcluster --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=nist --suite=nist --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=nist+ps --suite=nist --ps-protocol --experimental=collections/default.experimental

mysql-test/collections/test-bt-debug

-perl mysql-test-run.pl --force --timer --parallel=auto --comment=debug --skip-ndbcluster --skip-rpl --report-features --experimental=collections/default.experimental

mysql-test/collections/test-bt-fast

-perl mysql-test-run.pl --force --timer --parallel=auto --comment=ps  --skip-ndbcluster --ps-protocol --report-features --experimental=collections/default.experimental
-perl mysql-test-run.pl --force --timer --parallel=auto --comment=stress --suite=stress --experimental=collections/default.experimental