Since neutron gate already switched to -constraints target, we need to
keep those targets until we switch gate back to using targets without
the postfix.
This change effectively makes both types of targets identical.
Note: override install_command for venv, releasenotes, and cover targets
since corresponding gate jobs do not provide constraints file yet.
Also removed cover-constraints target since it would never work in gate
anyway.
Co-Authored-By: Ihar Hrachyshka <ihrachys@redhat.com>
Co-Authored-By: Andreas Jaeger <aj@suse.com>
Change-Id: Ica2d509df0c54496aba7cb3162565384cc5d34c8