service: don't take a command named like an option for one

A run/task/service whose command starts like an option without a ':'
lost its command, e.g. the example in finit.conf(5):

    run [2345] @joe:users logger "Hello world"

was registered as the log option, running "Hello world".  Same for
pidof, pidproxy, cgroupfs-mount, and in block format too.

The option parser matches with MATCH_CMD(), a prefix match, also for
the options with no trailing ':' to end the prefix: log, pid, cgroup,
respawn, nowarn, and the rest.

Match these against the whole token, allowing only the separator that
starts a value: "log:", "pid:", "cgroup." and "cgroup:".

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/ChangeLog.md

@@ -156,6 +156,9 @@ All relevant changes are documented in this file.
 - Fix #512: `--` in the `command` of a block-format .conf, it was taken as the
   start of the description, so `command = "cmd -- arg"` ran `cmd` with
   description `arg`.  Found by Alexandru Paniș
+- Fix a command whose name starts like a service option, e.g. `logger` or
+  `pidof`.  It was taken as the `log` or `pid` option and the next argument
+  ran as the command, which also broke the `logger` example in finit.conf(5)
 - Reject a .conf file that declares the same block title twice.  The title is
   the service identity and libConfuse merges two sections sharing one, so the
   file loaded as a single service holding a mix of both declarations,