(22651) add fixture access methods for example /proc/cpuinfo files

A common set of access methods for fixture example `/proc/cpuinfo` files
named `FacterSpec::Cpuinfo#cpuinfo_fixtures`
`FacterSpec::Cpuinfo#cpuinfo_fixture_read` and
`FacterSpec::Cpuinfo#cpuinfo_fixture_readlines`
Merge pull request #539 from jhoblitt/cpuinfo_fixture_consolidation_stable

(22651) add fixture access methods for example /proc/cpuinfo files