JDKW_TARGET does not support relative directories

[BrandonArp]

Running with JDKW_TARGET="./.jdkw_files" leads to the following errors:

[04:59:28] Unpacking tar.gz...
[04:59:28] tar -xzf "jdk-8.0.212-linux_x64.tar.gz"
[04:59:30] rm -f "jdk-8.0.212-linux_x64.tar.gz"
./.jdkw_files/jdkw/0.14.0/jdkw-impl.sh: 620: cannot create ./.jdkw_files/zulu_8.0.212_8.38.0.13_linux_x64/environment: Directory nonexistent
./.jdkw_files/jdkw/0.14.0/jdkw-impl.sh: 621: cannot create ./.jdkw_files/zulu_8.0.212_8.38.0.13_linux_x64/environment: Directory nonexistent
./.jdkw_files/jdkw/0.14.0/jdkw-impl.sh: 675: cannot create ./.jdkw_files/zulu_8.0.212_8.38.0.13_linux_x64/manifest.checksum: Directory nonexistent
[04:59:30] cd "/home/jenkins/agent/workspace/build-mad"
[04:59:30] Environment:
cat: ./.jdkw_files/zulu_8.0.212_8.38.0.13_linux_x64/environment: No such file or directory
./.jdkw_files/jdkw/0.14.0/jdkw-impl.sh: 684: .: Can't open ./.jdkw_files/zulu_8.0.212_8.38.0.13_linux_x64/environment

A fix could be resolving relative paths at execution start time and then using the resolved path.