Modify NiFiGroovyTest.groovy to avoid needing unlimited strength JCE policy

When running NiFiGroovyTest unit test when using a JDK that lacks unlimited strength JCE policy, the test fails.

 
[ERROR] testInitializePropertiesShouldSetBootstrapKeyFromFile(org.apache.nifi.NiFiGroovyTest)  Time elapsed: 0.121 s  <<< ERROR!
java.lang.IllegalArgumentException: There was an issue decrypting protected properties
at org.apache.nifi.NiFiGroovyTest.testInitializePropertiesShouldSetBootstrapKeyFromFile(NiFiGroovyTest.groovy:166)
Caused by: org.apache.nifi.properties.SensitivePropertyProtectionException: The key must be a valid hexadecimal key
at org.apache.nifi.NiFiGroovyTest.testInitializePropertiesShouldSetBootstrapKeyFromFile(NiFiGroovyTest.groovy:166)
 
The test uses a nifi.properties resource that does aes/gcm/256 encryption.