specfile: Add support for EL8

specfile: Add support for EL8

List of changes:

* ganglia-devel is not available in el8 yet
* gpsd-devel is not available in el8 yet
* libmodbus-devel is not available in el8 yet
* liboping-devel is not available in el8 yet
* mosquitto-devel is not available in el8 yet
* fix python dep in el8
* disable liblvm
* dependency problem while configuring smart
* add check_uptime
* simplify python rhel version logic and force python3 for rhel8
* remove support for EL<6
* disable redfish
* disable slurm
* disable intel dcpmm
* disable capabilities
* disable dpdk_telemetry
* disable ipstats
* disable varnish for el6
* disable smart for el6 and el8

TODO:

* buddyinfo
* logparser
* ubi
* write_influxdb_udp.so

Change-Id: I0bc5a723e3682e4f60e6c09670f286d20df507d5
Changelog: update specfile for EL8

Change-Id: Ic8ee01c69128f7bc4ec90a1d16a67b016a342b11

Change-Id: I80865415f1b056042f5b0d0c0c661c2e500a115d