Make the connector compatible with java-1.8.0-openjdk

[jfilak]

• the test results need to be updated (the test stack traces differs from the results : +/- frames, updated exception messages)
• memory issues need to be resolved (java-1.8 consumes more memory, thus we have to decrease the limits).
• HttpExchange.sendResponseHeaders() freezes

[jfilak]

Apart from the listed issues it seems that the transition to java-1.8.0-openjdk was smooth. Only 14% of tests fails with java 1.8.

[jfilak]

abrt-java-connector cannot be installed on Fedora 21 because java-1.7.0 is obsoleted.

[jfilak]

ITW has sorted out the hang issue with this commit: http://icedtea.classpath.org/hg/icedtea-web/rev/d700c395b040