Test fails for nifi-media-processors when decimals-separator != .

When building Nifi it fais a test in the nifi-media-processors component:

[*ERROR*] testExtractPNG(org.apache.nifi.processors.image.ExtractImageMetadataTest)  Time elapsed: 0.014 s  <<< FAILURE!

org.junit.ComparisonFailure: expected:<0[.]455> but was:<0[,]455>

at org.apache.nifi.processors.image.ExtractImageMetadataTest.testExtractPNG(ExtractImageMetadataTest.java:96)

It's trivial to fix, just make English the primary language, but perhaps the test can be more robust.