Makefile: Use 'command -v selinuxenabled' instead of hard-coded path
Makefile: Use 'command -v selinuxenabled' instead of hard-coded path

The hard-coded path landed in 488216f5 (Make sure selinuxenabled
exists before executing it, 2016-10-17, #154), but there's no need to
require that path.  Using 'command -v' (in POSIX [1]) supports anyone
who has selinuxenabled in their PATH.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

kubernetes-incubator/cri-o,nalind/cri-o,mikebrow/cri-o,nalind/cri-o,vbatts/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o,jwhonce/ocid,rhatdan/cri-o,kubernetes-incubator/ocid,mikebrow/cri-o,vbatts/cri-o,jwhonce/ocid,vbatts/cri-o,rhatdan/cri-o,mikebrow/cri-o,nalind/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,jwhonce/ocid,vbatts/cri-o,rhatdan/cri-o,rhatdan/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid