L3 agent's extensions list should be passed as an array
to the neutron::agents::l3 class and then it should be converted
to the comma separated string in the L3 agent's config.
This patch changes expected type of the variable and
adds that such conversion from an array to string.
Conflicts:
manifests/agents/l3.pp
Change-Id: I0650085d2aa2c3492b175c565976705c977fd806
(cherry picked from commit d29611f08a)
(cherry picked from commit db15124518)
(cherry picked from commit 9029fe04cc)
(cherry picked from commit 82324318ca)
367ba177f6