metrics: add missing exit on error path

Fixed null pointer dereference.

Reported by Coverity as CID #1127337
plugins/servlet: Check uwsgi_jvm_exception return value

Reported vy Coverity as CID #1125169.
plugins/xslt: fix memory leak

Reported by Coverity as CID #1125168
plugins/xslt: fail early if content_type is null

Fixes null pointer dereference.

Reported by Coverity as CID #1125161
core: fix memory leak

Reported by Coverity as CID #1100819
plugins/corerouter: fix memory leak

While at it reindent the code

Reported by Coverity as CID #1100818.
core: fix memory leak

Reported by Coverity as CID #1100813.
core/logging: if we cannot reopen the log exit

This fixes passing negative fds to write and lseek.

Reported by Coverity as CID #1100807.
Merge pull request #449 from xrmx/coverity0911-2

More coverity fixes