Add initial automated test for OSSEC alert using ossec-logtest
Add initial automated test for OSSEC alert using ossec-logtest

Verify that the log event describes in PR #871 (grsec denying RWX
mmap) produces an OSSEC alert of level 7.

Note: The rule added in PR #871 was later reverted, which is why
current SecureDrop produces OSSEC alerts for this kind of log
event.

conorsch/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,micahflee/securedrop,garrettr/securedrop,micahflee/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,garrettr/securedrop,micahflee/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,conorsch/securedrop,micahflee/securedrop,heartsucker/securedrop,garrettr/securedrop,conorsch/securedrop,conorsch/securedrop