[lxc-devel] Remove process_lock() except where actually needed

[Andrey Mazo]

This patchset is a follow-up to the pull request [1] summarizing a long discussion there.
First patch removes most of process_lock()/process_unlock() usage.
Second patch replaces getmntent() usage with getmntent_r() to ensure this piece is thread-safe.
These patches may be applied independently.

[1] https://github.com/lxc/lxc/pull/106