Fix multiple mount options not recognized

[dbw9580]

What changes are proposed in this pull request?

Fix multiple mount options specified by -o not recognized by Alluxio Fuse.
The -o option can be specified multiple times, and each time it can take a comma separated list of key=value mount options.

Why are the changes needed?

Fuse mounting with bin/alluxio-fuse mount hdfs://10.10.1.2:9000/ /work/alluxio_fuse -o kernel_cache -o attr_timeout=6000 -o entry_timeout=6000 errors with

Exception in thread "main" com.beust.jcommander.ParameterException: "-o": couldn't convert "kernel_cache,attr_timeout=6000,entry_timeout=6000" to a `key=value` pair because contains more than 1 `=`
	at alluxio.fuse.options.MountCliOptions$KvPairsConverter.convert(MountCliOptions.java:74)
	at alluxio.fuse.options.MountCliOptions$KvPairsConverter.convert(MountCliOptions.java:50)
	at com.beust.jcommander.JCommander.convertValue(JCommander.java:1333)
	at com.beust.jcommander.ParameterDescription.addValue(ParameterDescription.java:249)

The bash scripts concatenates the multiple occurrences of -o into a comma-separated list and passes it to the Java program. The PR does the other way around, preserving them and splitting the kv pair list in a -o option into multiple options.

Does this PR introduce any user facing changes?

No.

[huanghua78]

Looks good.

[huanghua78]

I have verified it works.

[dbw9580]

alluxio-bot, merge this please