ignited: catch signals and cleanup socket file

[chanwit]

This PR catches signals and cleans the left over socket file up.
Fixes #485

Result:

DEBU[0000] FileWatcher: Monitoring thread started       
DEBU[0000] SyncStorage: Monitoring thread started       
DEBU[0000] FileWatcher: Dispatch thread started         
DEBU[0000] GenericWatchStorage: Monitoring thread started 
INFO[0000] Starting GitOps loop for repo at "git@github.com:chanwit/ignited-demo" 
INFO[0000] Whenever changes are pushed to the master branch, Ignite will apply the desired state locally 
DEBU[0000] Starting the commit loop...                  
DEBU[0000] Starting the repo sync...                    
DEBU[0000] Starting the checkout loop...                
INFO[0000] Initializing the Git repo...                 
INFO[0026] Git initialized: A bare clone of repo "git@github.com:chanwit/ignited-demo" has been made 
INFO[0026] New commit observed on branch "master": a57fca1f35fd9c42598e2d97824900b0e2cd2115. User initiated: true 
INFO[0026] Initial clone done, entering the checkout loop... 
DEBU[0030] FileWatcher: Dispatch thread started         
DEBU[0030] FileWatcher: Monitoring thread started       
DEBU[0030] GenericWatchStorage: Monitoring thread started 
DEBU[0030] SyncStorage: Monitoring thread started       
DEBU[0030] GenericMappedRawStorage: AddMapping: "vm/022b373de5d34c80" -> "/tmp/flux-working982449342/myvm.yaml" 
DEBU[0030] SyncStorage: Received update {{MODIFY &TypeMeta{Kind:VM,APIVersion:ignite.weave.works/v1alpha2,}} 0xc000370240} true 
DEBU[0030] SyncStorage: Sent update: {MODIFY &TypeMeta{Kind:VM,APIVersion:ignite.weave.works/v1alpha2,}} 
DEBU[0030] FileWatcher: Skipping suspended event MODIFY for path: "/tmp/flux-working982449342/myvm.yaml" 
^CDEBU[0066] Signal SIGTERM caught                        
DEBU[0066] Socket "/var/lib/firecracker/daemon.sock" removed successfully 
DEBU[0066] Program normally terminated     

[chanwit]

cc @palemtnrider

[palemtnrider]

Just a few suggested changes. Thanks for fixing this.

[palemtnrider]

LGTM. Thanks for fixing this!

[chanwit]

Thank you @palemtnrider for reviewing this.
I'll have another PR for the dep changes.