Avoid add duplicate route in userdata ns
Avoid add duplicate route in userdata ns

Check route before add it. Avoid
"""
2017-09-26 09:42:10,147 WARNING [kvmagent.kvmagent] failed to execute
bash[ip netns exec br_em02_b1ed2381993e47c68b5eb868fb52602e ip r add
default dev inner8], return code: 2, stdout: , stderr: RTNETLINK
answers: File exists
"""

Closes ZSTAC-7160

live4thee/zstack-utility,zstackorg/zstack-utility,zstackio/zstack-utility,live4thee/zstack-utility,zstackorg/zstack-utility,live4thee/zstack-utility,zstackio/zstack-utility,zstackio/zstack-utility,zstackorg/zstack-utility