tools: Avoid errors when reading notifier.conf

The current mechanism that we use to read the notifier.conf file in the
notifier script generates the following error messages:

  engine-notifier.sh: line 68: declare: `#': not a valid identifier

To avoid that the condition to ignore empty lines and comment lines has
been replaced with a sed command that removes them before they are
processed by the notifier script.

Change-Id: If2670db513f6f9814feb8fe2786219f12530ea96
Bug-Url: https://bugzilla.redhat.com/911216
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>