[HatoholArmPluginInterface] Add a new method: sendInitiationRequest().
[HatoholArmPluginInterface] Handle HAPI_MSG_INITIATION_REQUEST.
[HatoholArmPluginGateTest] Fix a fail on the test.

When a packet received after the expected messsage is
received, the message is updated. As a result, the test fails.
This patch fixes the problem by ignoring the message after the
expected one is obtained.
[HatoholArmPluginInterface] Send initiation request soon after a plugin proecess starts.

For example, an passive arm-plugin process accidentally exits and
then an operator restarts it. The plugin process doesn't become ready state,
because initialization is not performed. Currently initialization packet
is sent from server (HatoholArmPluginGate) only when it starts.

With this patch, a plugin process requests to start initiation when it starts.
[HatoholArmPluginBase] Add a comment about a pottential problem.
Merge pull request #241 from project-hatohol/issue-171-11

Issue 171 11