fix the image name of collector issue and push docker images when skywalking is tagged and the branch is master

.travis.yml

@@ -1,3 +1,8 @@
+sudo: required
+
+services:
+  - docker
+
 language: java
 install:
   - cd ci-dependencies

skywalking-collector/skywalking-collector-worker/pom.xml

@@ -101,7 +101,7 @@
                 <version>${docker.plugin.version}</version>
                 <configuration>
                     <skipDocker>false</skipDocker>
-                    <imageName>${docker.cache.imageName}</imageName>
+                    <imageName>skywalking/${docker.cache.imageName}</imageName>
                     <imageTags>
                         <imageTag>${docker.imageTag.version}</imageTag>
                     </imageTags>

travis/push_image.sh

@@ -1,13 +1,19 @@
 #!/bin/sh
 
 check_pull_is_tagged() {
-  if [ "${TRAVIS_TAG}" = "" ]; then
+  if [ "${TRAVIS_TAG}" == "" ]; then
     return 1
   else
-    echo "Push the collector image of ${TRAVIS_TAG} version."
     return 0
   fi
+}
 
+check_branch_is_master(){
+    if [ "${TRAVIS_BRANCH}" == "master" ]; then
+        return 0;
+    else
+        return 1;
+    fi
 }
 
 push_collector_image() {
@@ -18,7 +24,7 @@ push_collector_image() {
 }
 
 
-if check_pull_is_tagged; then
+if check_pull_is_tagged && check_branch_is_master; then
     push_collector_image
     echo "Push is Done!"
 fi