autoconf: fix python2 checking and jons>=0.11
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 <e24f3acbe39bf94f92e8af3c48f8852106ad5ad7@redhat.com>

tasleson/libstoragemgmt,libstorage/libstoragemgmt,cathay4t/libstoragemgmt,jumitche/libstoragemgmt,lazy404/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,tasleson/libstoragemgmt,lazy404/libstoragemgmt,cathay4t/libstoragemgmt,joehandzik/libstoragemgmt,joehandzik/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt,libstorage/libstoragemgmt,cathay4t/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,joehandzik/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,tasleson/libstoragemgmt,cathay4t/libstoragemgmt,joehandzik/libstoragemgmt,lazy404/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,libstorage/libstoragemgmt,libstorage/libstoragemgmt,jumitche/libstoragemgmt,lazy404/libstoragemgmt,tasleson/libstoragemgmt,jumitche/libstoragemgmt,libstorage/libstoragemgmt