cirrus-ci: enable EPEL for CentOS 7
cirrus-ci: enable EPEL for CentOS 7

It used to be enabled by default, but not as of last few weeks.

While at it, add rpm -q command to make sure all required RPMS were in
fact installed (at least CentOS 7 yum exits with 0 when some packages
requested are not available).

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

opencontainers/runc,opencontainers/runc,opencontainers/runc,opencontainers/runc