[SQUASH] build: remove openjdk warning

build: Allow building with OpenJDK

My local builds with OpenJDK have been successful - no
reason to disallow it, let's go free...

Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>

Fix determination of java version

The script requires the java version to be on
line one of the output of `java -version`.
If you use _JAVA_OPTIONS to inject parameters
to each JVM, that will produce an output before
each VM is started, and the script won't be able
to find the java version, since `head -n 1` now
returns the wrong line. Grep for 'version' instead
to always get the right line from the output.

Change-Id: Iaf2798ba805d1b289b7e82239113b99479250dd8
Signed-off-by: Tim Roes <mail@timroes.de>

build/core: Remove useless warning when using OpenJDK

We provide and use a custom prebuilt OpenJDK 7 by default, so remove
this useless warning.

Change-Id: I61578c6b966bc72b328404c4a74e585a4f781d93
build: Set OpenJDK 1.7 as default java compiler

Change-Id: I8494669517169b8377f8ffaaa1cbe7356f38a139