api.c: avoid ambiguous controller name matches

api.c: avoid ambiguous controller name matches

calling "hasmntopt" to determine if the controller name exists in
"mntopt", may cause errors because of "hasmntopt" only match substring.

cpu controller may incorrectly match to cpuset when cpuset mount info
appeared before cpu,cpuacct in "/proc/mounts", so we need to validate
the last character to make sure the controller name matches exactly.

Signed-off-by: liupan <490021209@qq.com>
Reviewed-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>