sanity: use lsb distro_identifier

* distro_identifier returns lsb_data['Distributor ID']-lsb_data['Release']
  which in some cases is different then lsb_release -d -s, e.g.
  Distributor ID: Ubuntu
  Description:    Ubuntu 12.04 LTS
  Release:        12.04
  Codename:       precise
  But we probably don't need to sanity list each point release in LTS
  and sstate is already using distro_identifier as prefix for native
  sstate archives
* This will need update to SANITY_TESTED_DISTROS (at least
  s/Ubuntu 12.04 LTS/Ubuntu-12.04/g etc), that's why sending as RFC
  first.

(From OE-Core rev: a32ea459ca168792161af2d521a14fe00cffb4b3)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sanity.bbclass

@@ -280,11 +280,8 @@ def check_supported_distro(sanity_data):
             f.close()
     else:
         # Use LSB method
-        import subprocess as sub
         try:
-            p = sub.Popen(['lsb_release','-d','-s'],stdout=sub.PIPE,stderr=sub.PIPE)
-            out, err = p.communicate()
-            distro = out.rstrip()
+            distro = oe.lsb.distro_identifier()
         except Exception:
             distro = None