check-procs.rb: Reasonable matching conditions

check-procs should check if any matching processes exist when no
thresholds are specified.

* Remove the default upper thresholds (-w and -c)
* Change lower thresholds (-W and -C) to 1 instead of 0

Suppose we have 9 ssh processes running and any processes don't
mach to 'foo'. With this patch, we'll get this result:

    % ./plugins/processes/check-procs.rb -p ssh
    CheckProcs OK: Found 9 matching processes; cmd /ssh/
    % ./plugins/processes/check-procs.rb -p ssh -w 5 -c 10
    CheckProcs WARNING: Found 9 matching processes; cmd /ssh/
    % ./plugins/processes/check-procs.rb -p foo
    CheckProcs CRITICAL: Found 0 matching processes; cmd /foo/
    % ./plugins/processes/check-procs.rb -p foo -C 0
    CheckProcs WARNING: Found 0 matching processes; cmd /foo/
    % ./plugins/processes/check-procs.rb -p foo -W 0 -C 0
    CheckProcs OK: Found 0 matching processes; cmd /foo/
check-procs.rb: Revert unnecessary changes
Merge pull request #460 from maoe/fix-check-procs-defaults

check-procs.rb: Reasonable matching conditions