Changed nfdump_str
Fix network and ceilometer plugin

- Fix remote commands for nfdump
- Change error to warning in ceilometer plugin
Fix network plugin

- Remove stderr.read() from nf_dump command execte. It just hanging plugin.
Change default date in pricing_statistics to yesterday

- Change default date in pricing_statistics to yesterday
Merge pull request #145 from kula1922/hotfix/fix-network-collect-plugin

Hotfix/fix network collect plugin
Merge pull request #146 from kula1922/hotfix/change-default-date-in-pricing-statistics

Change default date in pricing_statistics to yesterday