Issue Summary

This is reproducible on Data Center: (yes) 

Steps to Reproduce

1. Navigate to the Manage Apps section and download/install any plugin. For example: ScriptRunner.
2. Once the plugin is installed, navigate to the directory <JIRA_HOME>/plugins/installed-plugins and you will notice that the jar is downloaded with name like: plugin.3504767825672828476.download.jar. 
3. Notice that it has no mention of the plugin name.
4. If we download the jar manually from marketplace.atlassian.com and upload it using Upload App button, it gets added with the plugin name instead of random numbers as pointed in Point 2 above.

Expected Results

Installing any plugin from Manage Apps section should copy the jar name under <JIRA_HOME>/plugins/installed-plugins with the plugin/app name. It is helpful in determining what jar belong to what plugin. 

Actual Results

Refer to the Jars highlighted in the red box below:

Workaround

Use the Upload App button under Manage Apps section to get the jar downloaded with correct name.

If you'd like to only view the app names for each JAR, then run these commands:

cd <shared-home>/plugins/installed-plugins
for i in $(find . -name "plugin.*.download.jar"); do echo $i; unzip -p $i  atlassian-plugin.xml | grep -Eo "atlassian-plugin [^>]*>" | sed -E 's/(atlassian-plugin)|(plugins-version=".")|(>)//g'; done 

The output should resemble something like this one below, listing the file names and corresponding app names.

./plugin.9834594699245328574.download.jar
 key="com.javahollic.jira.jemh-ui" name="Enterprise Mail Handler (JEMH) for Jira Data Center" 
./plugin.8297165867298969457.download.jar
 key="com.qotilabs.jira.rich-filters-plugin" name="Rich Filters for Jira Dashboards" 
./plugin.6287285435938084735.download.jar
 key="com.atlassian.jira.plugins.jira-slack-server-integration-plugin" name="Slack for Jira Data Center" 
./plugin.532409277185381002.download.jar
 key="rw-smart-checklist-biz" name="Smart Checklist" 
./plugin.5986725383647808491.download.jar
 key="com.stonikbyte.great.gadgets.server" name="Great Gadgets" 
./plugin.16432350874212133862.download.jar
 key="com.codebarrel.addons.automation" name="Automation for Jira" 
./plugin.16246789332246523104.download.jar
 key="com.xpandit.plugins.xray" name="Xray"