* Rename IgnoreListPath to MountInfoPath in config & constants
The string points to /proc/self/mountinfo
* fs_util_test.go: fix tests failing when /tmp mountpoint present
The tests
* Test_GetFSFromLayers_ignorelist
* Test_GetFSFromLayers_with_whiteouts_include_whiteout_disabled
* Test_GetFSFromLayers_with_whiteouts_include_whiteout_enabled
were failing on systems with a /tmp mountpoint:
fs_util.InitIgnoreList() adds all mountpoints to the ignore list,
but the tests were expecting file operations in a /tmp subdirectory.
This change provides an empty mountinfo list for the affected tests.
Fixes#1779