use revision in pom.xml of dubbo-metadata-report-etcd

[zhaixiaoxiang]

What is the purpose of the change

change 2.7.2-SNAPSHOT to revision in pom.xml of dubbo-metadata-report-etcd, otherwise there are maven package failures as following:

[INFO] Scanning for projects...
[ERROR] [ERROR] Some problems were encountered while processing the POMs:
[FATAL] Non-resolvable parent POM for org.apache.dubbo:dubbo-metadata-report-etcd:2.7.2-SNAPSHOT: Could not find artifact org.apache.dubbo:dubbo-metadata-report:pom:2.7.2-SNAPSHOT and 'parent.relativePath' points at wrong local POM @ line 22, column 13
 @ 
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]   
[ERROR]   The project org.apache.dubbo:dubbo-metadata-report-etcd:2.7.2-SNAPSHOT (~/gh-incubator-dubbo/dubbo-metadata-report/dubbo-metadata-report-etcd/pom.xml) has 1 error
[ERROR]     Non-resolvable parent POM for org.apache.dubbo:dubbo-metadata-report-etcd:2.7.2-SNAPSHOT: Could not find artifact org.apache.dubbo:dubbo-metadata-report:pom:2.7.2-SNAPSHOT and 'parent.relativePath' points at wrong local POM @ line 22, column 13 -> [Help 2]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildingException
[ERROR] [Help 2] http://cwiki.apache.org/confluence/display/MAVEN/UnresolvableModelException

[codecov-io]

Codecov Report

Merging #3980 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3980      +/-   ##
============================================
+ Coverage     63.82%   63.85%   +0.02%     
  Complexity       71       71              
============================================
  Files           722      722              
  Lines         31812    31852      +40     
  Branches       5088     5115      +27     
============================================
+ Hits          20305    20340      +35     
- Misses         9165     9175      +10     
+ Partials       2342     2337       -5

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	64.1% <0%> (-17.95%)	0% <0%> (ø)
...dubbo/common/status/support/LoadStatusChecker.java	46.15% <0%> (-3.85%)	0% <0%> (ø)
...bo/rpc/cluster/support/FailbackClusterInvoker.java	67.21% <0%> (-3.28%)	0% <0%> (ø)
...ting/exchange/support/header/HeartbeatHandler.java	83.72% <0%> (-2%)	0% <0%> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	80.07% <0%> (-1.54%)	0% <0%> (ø)
.../remoting/transport/netty4/NettyClientHandler.java	68.42% <0%> (-1.23%)	0% <0%> (ø)
...he/dubbo/remoting/transport/netty/NettyClient.java	66.1% <0%> (-1.14%)	0% <0%> (ø)
...e/dubbo/remoting/transport/netty4/NettyClient.java	70.58% <0%> (-1.06%)	0% <0%> (ø)
...ache/dubbo/remoting/transport/mina/MinaClient.java	58.46% <0%> (-0.92%)	0% <0%> (ø)
.../main/java/org/apache/dubbo/qos/textui/TTable.java	83.79% <0%> (-0.87%)	0% <0%> (ø)
... and 25 more

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[lovepoem]

LGTM