cpu plugin: Fix parsing of SoftIRQ under Linux.
swap plugin: Make SwapCached optional under Linux.

OpenVZ doesn't provide the line, which caused swap collection to be
skipped entirely on these systems. Instead, "cached" should simply be
ignored, as it is on other systems. Thanks to @zerkms for reporting this
problem!

Fixes: #733
Merge branch 'master' into debian
updating build.sh results