autoconf: fix python2 checking and jons>=0.11

 * Try to locate python in the sequence of:
    python2.7 python 2.6 python2 python
   Then check python version as we only support python 2.

 * Pkconfig will try 'json.pc' if 'json-c.pc' failed.

Tested by OBS.
Manually tested by './configure && make check' on:
 * Archlinux
 * Fedora 20
 * RHEL 6.5
 * RHEL 7.0

Signed-off-by: Gris Ge <fge@redhat.com>
lsm REST daemon: Fix json-c include header path for json>=0.11

Some platform(like Archlinux, json-c-0.12), does not store header in json
folder.

Use 'json.h' instead of 'json/json.h' and let autotools handle it.

Signed-off-by: Gris Ge <fge@redhat.com>
force using python2

The '/usr/bin/python' of some platform like Archlinux is actually python3.

Currently none of our python codes is tested on python3, hence forcing to use
python2.

Signed-off-by: Gris Ge <fge@redhat.com>
lsmenv: Remove experimental smart match code

The smart match '~~' is marked as experimental since perl 5.18.
We replaced it with is_in_array() subroutine.

Signed-off-by: Gris Ge <fge@redhat.com>