slaprunner: ~/bin/slapos: don't override SLAPOS_CONFIGURATION

Because this slapos often is executed when just running `slapos` at is
in the $PATH, we should also consider special cases where users want to
call this script with another $SLAPOS_CONFIGURATION.

When $SLAPOS_CONFIGURATION is already set, ~/bin/slapos will not change
it, it will only set it when not set.

software/slaprunner/buildout.hash.cfg

@@ -78,4 +78,4 @@ md5sum = 2451072826a9ad9425d62c9e9c7f6284
 
 [template-slapuser-script]
 filename = template/slapos-slapuser-script.in
-md5sum = becafae59ab9973724e0edb238f4cb7a
+md5sum = 2e5fdd6e8e07429f83a38b148b2f1cb0

software/slaprunner/template/slapos-slapuser-script.in

 #!/bin/sh
 # run slapos command inside slaprunner with appropriate config
 
-SLAPOS_CONFIGURATION={{ config_location }}   \
-SLAPOS_CLIENT_CONFIGURATION=$SLAPOS_CONFIGURATION   \
+export SLAPOS_CONFIGURATION=${SLAPOS_CONFIGURATION-"{{ config_location }}"}
+export SLAPOS_CLIENT_CONFIGURATION=${SLAPOS_CLIENT_CONFIGURATION-$SLAPOS_CONFIGURATION}
 exec {{ slapos_python_file_location }} "$@"