update the agent version to 2.1.5.rc3 (Azure#286)

Update version to 2.1.5.rc2 (Azure#273)

* update agent version to 2.1.5.rc1

Remove unused import

upgrade to 2.0.18

support the centos 7.x

fix the default route issue.

Update version to WALinuxAgent-2.0.18.rc5

Update version to WALinuxAgent-2.0.18.rc4

Fix ClientAliveInterval setting in sshd_config.

yum clean all before search for packages.