Rewrite groovy tests as junit

[tdrwenski]

Description of Changes

Closes #1188.

1. Rewrites groovy/spock tests as junit:

cdm/core/src/test/groovy/ucar/nc2/ft/point/FlattenedDatasetPointCollectionSpec.groovy
cdm/core/src/test/groovy/ucar/nc2/ft/point/PointIteratorFilteredSpec.groovy 
cdm/core/src/test/groovy/ucar/nc2/ft2/coverage/HorizCoordSysCrossSeamBoundarySpec.groovy
cdm/core/src/test/groovy/ucar/nc2/util/cache/ReacquireClosedDatasetSpec.groovy 
netcdf4/src/test/groovy/ucar/nc2/jni/netcdf/Nc4IospMiscSpec.groovy
netcdf4/src/unloadedTest/groovy/ucar/nc2/jni/netcdf/UnloadedNc4IospSpec.groovy

Note that for Nc4IospMiscSpec.groovy, some private members were being tested so I had to make them package private in order to keep the test as is.

2. Deletes:

./legacy/src/test/groovy/thredds/crawlabledataset/s3/ThreddsS3ClientImplSpec.groovy
./legacy/src/test/groovy/thredds/crawlabledataset/s3/CachingThreddsS3ClientSpec.groovy
./legacy/src/test/groovy/thredds/crawlabledataset/s3/CrawlableDatasetAmazonS3Spec.groovy
./legacy/src/test/groovy/thredds/crawlabledataset/s3/S3URISpec.groovy

as these are testing legacy code.

3. Removes all groovy/ Spock dependencies.