packaging: spec: add support for EL7 builds

Change-Id: I1672e50c4977b4fb1ad97da9e661d5794b11d1e9
Bug-Url: https://bugzilla.redhat.com/1159293
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
packaging: spec: update spec syntax

Solves:
 ***************************************************************
 * WARNING!  mvn-rpmbuild is deprecated and it will be removed *
 * in future.  Users should migrate to using %mvn_build macro  *
 * or call XMvn directly if greater flexibility is required.   *
 ***************************************************************

Change-Id: Ib81f345772db5da4d23cf1ee917b3d11e85b3ed6
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
packaging: fixes a warning while building

[WARNING]
[WARNING] Some problems were encountered while building the effective
model for
org.ovirt.engine.sdk:ovirt-engine-sdk-java:jar:3.6.0.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for
org.apache.maven.plugins:maven-eclipse-plugin is missing. @ line 143,
column 25
[WARNING]
[WARNING] It is highly recommended to fix these problems because they
threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support
building such malformed projects.
[WARNING]

Change-Id: I2924b7deb5b712e472721ea53bfa8d87513e2516
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>