Enable GPG signing of "solaris simple" builds

[sxa]

With the use of a proxy implementation for building Solaris we do not currently GPG signing enabled which is done as a separate job. It is likely that the best option for this is to create a short piece of pipeline code which can invoke the GPG signing and copy the artifacts back to a common place afterwards.

This could also invoke the simpltest jobs, which would probably tie it together with the build job in a more effective manner.

[sxa]

This is done and working as a phase in the simplepipe jobs.