common.rc has some complicated logic to find the common.config that
dates back to xfstests and is completely unnecessary now.  Just include
the contents of the file.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220505094723.732116-1-pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>