Fix folder structure for ic-amqp-plugin and ic-filter-plugin

Hi Guys

This path fix the folder structure for ic-amqp-plugin and ic-filter-plugin 
and change the package format from `tar` to `zip`

See https://github.com/pentaho/marketplace-metadata/pull/57
```
unzip -Z -1 ic-amqp-plugin-pdi-1.1.1-SNAPSHOT.zip 
ic-amqp-plugin/
ic-amqp-plugin/ic-amqp-plugin.jar
ic-amqp-plugin/logo.png
ic-amqp-plugin/plugin.xml
```
```
unzip -Z -1  ic-filter-plugin-pdi-1.8.1-SNAPSHOT.zip 
ic-filter-plugin/
ic-filter-plugin/ic-filter-plugin.jar
ic-filter-plugin/lib/***.jar
ic-filter-plugin/logo.png
ic-filter-plugin/plugin.xml
```