1. Configuration adds new method `getEnumSet()` to get a set of enum values from
a configuration string.
<E extends Enum<E>> EnumSet<E> getEnumSet(String key, Class<E> enumClass, boolean ignoreUnknown)
Whitespace is ignored, case is ignored and the value "*" is mapped to "all values of the enum".
If "ignoreUnknown" is true then when parsing, unknown values are ignored.
This is recommended for forward compatiblity with later versions.
2. This support is implemented in org.apache.hadoop.fs.s3a.impl.ConfigurationHelper -it can be used
elsewhere in the hadoop codebase.
3. A new private FlagSet class in hadoop common manages a set of enum flags.
It implements StreamCapabilities and can be probed for a specific option being set
(with a prefix)
S3A adds an option fs.s3a.performance.flags which builds a FlagSet with enum
type PerformanceFlagEnum
* which initially contains {Create, Delete, Mkdir, Open}
* the existing fs.s3a.create.performance option sets the flag "Create".
* tests which configure fs.s3a.create.performance MUST clear
fs.s3a.performance.flags in test setup.
Future performance flags are planned, with different levels of safety
and/or backwards compatibility.
Contributed by Steve Loughran
a5806a9e7b