pmsignal: provide a targetted program mode
Provide a pmsignal mode which uses PCP_RUN_DIR pidfiles to
more reliably find only long-running PCP daemon processes,
rather than the shotgun approach of "killall" (while still
keeping the convenience of specifying programs by name).
Several of the daemon rc scripts are updated to use this
mode, to tackle Fedora BZ
1210976, and the recently added
pmieconf PMDA status check rule is also updated to use it.
Man page for pmsignal is fleshed out a bit (including some
missing text for existing options), and test 881 exercises
the functionality.