When parsing mount options e.g. from lxc.mount.entry the specified
options are mapped to the flags constants. To do so, the strings
are compared to the options contained in mount_opt. However,
when comparing the strings, the length of the string is not
checked. That entails that the option "rootcontext=selinux-context"
is mapped to the mount option read-only (ro). This commit fixes
this issue by checking if a '=' is contained in the specified option
and additionally comparing the length of the strings.
Signed-off-by: Maximilian Blenk <Maximilian.Blenk@bmw.de>