Trim newline from gdash config

Add the "-" trim marker to the erb stanza that generates the
deploy_addon gdash option so that the resulting configuration does not
include an embedded newline. Without this change the setting ends up
looking something like "alias(...)&alias(...)&alias(...)\n" in the
generated gdash.yaml file.

Change-Id: Ie646e8e2b0f00e527e751c890a300aac389c3769