lib/oe/lsb: attempt to ensure consistent distro id regardless of source

lib/oe/lsb: attempt to ensure consistent distro id regardless of source

The LSB Distributor ID and os-release NAME differ for most of the
distributions tested by the Yocto Project (CentOS, Debian, Fedora,
openSUSE and Ubuntu) however for all but openSUSE the os-release ID
matches the LSB Distributor ID when both are lowered before
comparison.

Therefore, in order to improve the consistency of identification of
a distribution, switch to using the os-release ID and converting
the ID value to lowercase.

Table showing comparison of LSB Distributor ID to os-release fields NAME
and ID for current Yocto Project supported host distributions:

Distribution | Version | Distributor ID   | NAME             | ID       |
-------------------------------------------------------------------------
CentOS       | 7       | CentOS           | CentOS Linux     | centos   |
Debian       | 8       | Debian           | Debian GNU/Linux | debian   |
Fedora       | 23      | Fedora           | Fedora           | fedora   |
Fedora       | 24      | Fedora           | Fedora           | fedora   |
openSUSE     | 13.2    | openSUSE project | openSUSE         | opensuse |
openSUSE     | 42.1    | SUSE LINUX       | openSUSE Leap    | opensuse |
Ubuntu       | 14.04   | Ubuntu           | Ubuntu           | ubuntu   |
Ubuntu       | 16.04   | Ubuntu           | Ubuntu           | ubuntu   |

[YOCTO #10591]

Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>