[SMALLFIX] Support enter debug mode use `-debug`
[SMALLFIX] Support enter debug mode use `-debug`

example:
if you append append the `ALLUXIO_SHELL_DEBUG_JAVA_OPTS` in `alluxio-env.sh` as following:
```bash
ALLUXIO_SHELL_DEBUG_JAVA_OPTS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=5603"
```
then you can execute your shell command with -debug between the alluxio COMMAND and GENERIC_COMMAND_OPTIONS
```bash
$ alluxio fs -debug ls /
debug mode!
Listening for transport dt_socket at address: 5603
```
calvinjia/tachyon,Alluxio/alluxio,maobaolong/alluxio,madanadit/alluxio,Alluxio/alluxio,wwjiang007/alluxio,uronce-cc/alluxio,calvinjia/tachyon,bf8086/alluxio,Reidddddd/alluxio,maboelhassan/alluxio,WilliamZapata/alluxio,yuluo-ding/alluxio,maboelhassan/alluxio,Alluxio/alluxio,calvinjia/tachyon,calvinjia/tachyon,maobaolong/alluxio,jsimsa/alluxio,maobaolong/alluxio,Reidddddd/mo-alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,jsimsa/alluxio,riversand963/alluxio,jsimsa/alluxio,riversand963/alluxio,calvinjia/tachyon,wwjiang007/alluxio,EvilMcJerkface/alluxio,EvilMcJerkface/alluxio,riversand963/alluxio,Reidddddd/mo-alluxio,EvilMcJerkface/alluxio,WilliamZapata/alluxio,Alluxio/alluxio,ChangerYoung/alluxio,maboelhassan/alluxio,aaudiber/alluxio,PasaLab/tachyon,wwjiang007/alluxio,PasaLab/tachyon,aaudiber/alluxio,maobaolong/alluxio,PasaLab/tachyon,ShailShah/alluxio,PasaLab/tachyon,ShailShah/alluxio,EvilMcJerkface/alluxio,ShailShah/alluxio,jsimsa/alluxio,riversand963/alluxio,jswudi/alluxio,madanadit/alluxio,ChangerYoung/alluxio,apc999/alluxio,bf8086/alluxio,bf8086/alluxio,wwjiang007/alluxio,WilliamZapata/alluxio,Alluxio/alluxio,madanadit/alluxio,maboelhassan/alluxio,Alluxio/alluxio,calvinjia/tachyon,bf8086/alluxio,apc999/alluxio,maobaolong/alluxio,aaudiber/alluxio,yuluo-ding/alluxio,PasaLab/tachyon,wwjiang007/alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,aaudiber/alluxio,bf8086/alluxio,madanadit/alluxio,Reidddddd/alluxio,madanadit/alluxio,Reidddddd/mo-alluxio,jswudi/alluxio,madanadit/alluxio,ChangerYoung/alluxio,ChangerYoung/alluxio,madanadit/alluxio,bf8086/alluxio,apc999/alluxio,uronce-cc/alluxio,WilliamZapata/alluxio,aaudiber/alluxio,yuluo-ding/alluxio,Alluxio/alluxio,wwjiang007/alluxio,madanadit/alluxio,jswudi/alluxio,wwjiang007/alluxio,maobaolong/alluxio,Reidddddd/alluxio,ShailShah/alluxio,apc999/alluxio,wwjiang007/alluxio,jswudi/alluxio,jswudi/alluxio,bf8086/alluxio,maobaolong/alluxio,WilliamZapata/alluxio,Alluxio/alluxio,uronce-cc/alluxio,maboelhassan/alluxio,Reidddddd/mo-alluxio,apc999/alluxio,PasaLab/tachyon,jswudi/alluxio,riversand963/alluxio,PasaLab/tachyon,ShailShah/alluxio,yuluo-ding/alluxio,calvinjia/tachyon,Reidddddd/mo-alluxio,aaudiber/alluxio,jsimsa/alluxio,ShailShah/alluxio,Reidddddd/alluxio,jsimsa/alluxio,Reidddddd/alluxio,yuluo-ding/alluxio,Alluxio/alluxio,bf8086/alluxio,riversand963/alluxio,EvilMcJerkface/alluxio,wwjiang007/alluxio,maboelhassan/alluxio,EvilMcJerkface/alluxio,calvinjia/tachyon,maobaolong/alluxio,apc999/alluxio,Alluxio/alluxio,Reidddddd/mo-alluxio,aaudiber/alluxio,WilliamZapata/alluxio,uronce-cc/alluxio,ChangerYoung/alluxio,ChangerYoung/alluxio,yuluo-ding/alluxio,maboelhassan/alluxio,uronce-cc/alluxio,apc999/alluxio,Reidddddd/alluxio,wwjiang007/alluxio,uronce-cc/alluxio,Reidddddd/alluxio