S3A: option "fs.s3a.performance.flags" to take list of performance flags

HADOOP-19072 shows we want to add more optimisations than that of HADOOP-18930.

• Extending the new optimisations to the existing option is brittle
• Adding explicit options for each feature gets complext fast.

Proposed

• A new class S3APerformanceFlags keeps all the flags
• it build this from a string[] of values, which can be extracted from getConf(),
• and it can also support a "*" option to mean "everything"
• this class can also be handed off to hasPathCapability() and do the right thing.

Proposed optimisations

• create file (we will hook up HADOOP-18930)
• mkdir (HADOOP-19072)
• delete (probe for parent path)
• rename (probe for source path)

We could think of more, with different names, later.
The goal is make it possible to strip out every HTTP request we do for safety/posix compliance, so applications have the option of turning off what they don't need.