DAOS-16629 build: Allow separate test builds

[jolivier23]

Client and server tests require different packages. Separate test target so it doesn't imply client or server. It requires one or the other but this
allows building just client or server tests.

Required-githooks: true

Before requesting gatekeeper:

• Two review approvals and any prior change requests have been resolved.
• Testing is complete and all tests passed or there is a reason documented in the PR why it should be force landed and forced-landing tag is set.
• Features: (or Test-tag*) commit pragma was used or there is a reason documented that there are no appropriate tags for this PR.
• Commit messages follows the guidelines outlined here.
• Any tests skipped by the ticket being addressed have been run and passed in the PR.

Gatekeeper:

• You are the appropriate gatekeeper to be landing the patch.
• The PR has 2 reviews by people familiar with the code, including appropriate owners.
• Githooks were used. If not, request that user install them and check copyright dates.
• Checkpatch issues are resolved. Pay particular attention to ones that will show up on future PRs.
• All builds have passed. Check non-required builds for any new compiler warnings.
• Sufficient testing is done. Check feature pragmas and test tags and that tests skipped for the ticket are run and now pass with the changes.
• If applicable, the PR has addressed any potential version compatibility issues.
• Check the target branch. If it is master branch, should the PR go to a feature branch? If it is a release branch, does it have merge approval in the JIRA ticket.
• Extra checks if forced landing is requested
  • Review comments are sufficiently resolved, particularly by prior reviewers that requested changes.
  • No new NLT or valgrind warnings. Check the classic view.
  • Quick-build or Quick-functional is not used.
• Fix the commit message upon landing. Check the standard here. Edit it to create a single commit. If necessary, ask submitter for a new summary.

[github-actions]

Ticket title is 'Allow build of client and server tests separately'
Status is 'Open'
https://daosio.atlassian.net/browse/DAOS-16629

[ashleypittman]

Minor but you could just Import prereqs here.

Suggested change

	def build_tests(env, prereqs):
	"""build the tests"""
	Import('libdaos_tgts', 'cmd_parser')
	def build_tests(env):
	"""build the tests"""
	Import('libdaos_tgts', 'cmd_parser', 'prereqs`)