Enable haveged support in 'debops.apt' test

This should make GPG key generation faster on Travis-CI which is
notoriously poor in randomness department.
Move inventories one level down

All inventories will now be in <role-name>/inventory/ directory.
Fix test for ansible-ntp

- change the name of the main binary;
- look for a running ntpd process;
Fix the ntp test once more
Drop the path ceck from ntp test
Change the debops.ntp test conditions

debops.ntp role does not install OpenNTPD on OpenVZ/LXC containers, so
instead of testing if it's installed, let's test if it's not installed.
Also, set the timezone and check if it's correctly configured.
Add prepared GnuPG repository key to ansible-apt

This should fix problems with GPG key generation timing out on Travis.
Add more test conditions for ansible-apt role
Add more test conditions for ansible-auth
Update test conditions for ansible-apt_preferences
Fix mismatched paren in a test case
Change the way apt preferences are displayed
Check APT policy instead of list of packages

This should better show what preferences have been set.
Try different way of checking APT preferences
More changes in test of ansible-apt_preferences
Disable idempotency check in ansible-debug
Update test for ansible-etc_services
More changes in tests of ansible-etc_services
Change test type in ansible-etc_services
Refine test suite for ansible-etherpad