golang: +go1.17 -go1.15

Go1.17 is incremental improvement over Go1.16 with better and faster compiler,
runtime, module-mode improvements and faster generated code:

https://blog.golang.org/go1.17
https://golang.org/doc/go1.17

Drop support for Go1.15, as that release reached EOL and nothing currently uses
it in SlapOS.

Don't drop support for Go1.12 yet, as that long-ago-EOL and no longer supported
Go release is still being used by software/gitlab.

Remain default at Go1.16 yet.

Switch helloworld to Go1.17 and test this patch on that
software-release.

component/golang/buildout.cfg

@@ -42,15 +42,6 @@ md5sum = 6b607fc795391dc609ffd79ebf41f080
 environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
-[golang1.15]
-<= golang-common
-url = https://golang.org/dl/go1.15.12.src.tar.gz
-md5sum = b3a5dafa7028fa00083ce4aeaf5bcb9a
-
-# go1.15 needs go1.4 to bootstrap
-environment-extra =
-  GOROOT_BOOTSTRAP=${golang14:location}
-
 [golang1.16]
 <= golang-common
 url = https://golang.org/dl/go1.16.8.src.tar.gz
@@ -60,6 +51,14 @@ md5sum = 92e69a5e1bb6ea5e7498d12d03160032
 environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
+[golang1.17]
+<= golang-common
+url = https://golang.org/dl/go1.17.1.src.tar.gz
+md5sum = a78205838c2a7054522cb91c12982f26
+
+# go1.17 needs go1.4 to bootstrap
+environment-extra =
+  GOROOT_BOOTSTRAP=${golang14:location}
 
 # ---- infrastructure to build Go workspaces / projects ----
 

software/helloworld/software.cfg

@@ -32,6 +32,9 @@ parts =
 [python]
 part = python3
 
+[gowork]
+golang = ${golang1.17:location}
+
 # Macro for jinja templates. The filename is set in buildout.hash.cfg
 # in the section using this template
 [jinja-template]