update SSL cipher list for gerrit to support PFS

this is the same list of ciphers we use
on the main cluster nginx frontends since
recently (I830bec497338a36f)

also use it for gerrit to support
Forward Secrecy

bug: 53259
Change-Id: I00c436b157a63e19f2c0a42898100bdc664b723f
Merge "update SSL cipher list for gerrit to support PFS" into production