logging: Add .log to samples and update asterisk.logrotate.

Added .log extension to the sample logs in logger.conf.sample so that
they will be able to be opened in the browser when attached to JIRA
tickets. Because of this, asterisk.logrotate has also been updated to
look for .log extensions instead of no extension for log files such as
full and messages.

Change-Id: I5de743c03f08047d6c6cc80cac5019ae0c4c200f