Bugfix:
- "-a" option did not work.
- Some plugin doens not return value. That is why dummy vlaue will be set with zero by this program.

Improvement:
- Added PATH: Some plugins will call a program in "/usr/sbin" like ntp_offset plugin.
- ignore some plugins unsupported by this program.
  - diskstats
  - yum
- added ignore option.
- Some plugins output error. These messages should be ignored.
Merge pull request #3 from kunitake/release-0.05

Release 0.05