JDK-8180745: Add --release 10 as an alias for --release 9

[Jan Lahoda]

Hi,

In the JDK 10 repositories, several tests are failing:
langtools/tools/javac/options/release/ReleaseOptionUnsupported.java
langtools/tools/jdeprscan/tests/jdk/jdeprscan/TestNotFound.java
langtools/tools/jdeprscan/tests/jdk/jdeprscan/TestRelease.java

The proposed solution here is to reintroduce --release 10 as an alias to 
--release 9 until a proper fix is made (which will be JDK-8180744).

Bug:
https://bugs.openjdk.java.net/browse/JDK-8180745

Webrev:
http://cr.openjdk.java.net/~jlahoda/8180745/webrev.00/

Feedback is welcome.

Thanks,
     Jan