Jenkins config: autobuild and test openwrt-builddeps

[alexlist]

Automatically build openwrt-builddeps package and test install on supported platforms.

Initial targets:

Stable:
Ubuntu Trusty amd64 (14.04 LTS)
Debian Wheezy amd64 (7.6)

Testing/Development:
Ubuntu Utopic amd64 (14.10)
Debian Jessie amd64 (testing)
Debian sid amd64 (unstable)