### What changes were proposed in this pull request?
- gauge method definition improvement. i.e.
before
```
def addGauge[T](name: String, f: Unit => T, labels: Map[String, String])
```
after
```
def addGauge[T](name: String, labels: Map[String, String])(f: () => T)
```
which improves the caller-side code style
```
addGauge(name, labels) { () =>
...
}
```
- remove unnecessary Java/Scala collection conversion. Since Scala 2.11 does not support SAM, the extra implicit function is required.
- leverage Logging to defer message evaluation
- UPPER_CASE string constants
### Why are the changes needed?
Improve code quality and performance(maybe)
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Pass GA.
Closes#1670 from pan3793/CELEBORN-757.
Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
a1be02b4fa