Update a deployment health check status only its changed.

[tejal29]

relates to #176

In this PR,

No user affecting changes.

Add 2 methods to Deployment to

1. ReportLastSinceUpdated will return status if its updated.
2. Updated will only update status if it was changed.

[tejal29]

kokoko failure due to jib grade cyclic dependency:

            FAILURE: Build failed with an exception.
            
            * What went wrong:
            A problem occurred configuring root project 'workspace'.
            > Could not resolve all artifacts for configuration ':classpath'.
               > Could not resolve com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava.
                 Required by:
                     project : > com.google.cloud.tools.jib:com.google.cloud.tools.jib.gradle.plugin:1.5.0 > gradle.plugin.com.google.cloud.tools:jib-gradle-plugin:1.5.0 > com.google.guava:guava:28.0-jre
                  > Skipped due to earlier error
               > Could not resolve org.codehaus.mojo:animal-sniffer-annotations:1.17.
                 Required by:
                     project : > com.google.cloud.tools.jib:com.google.cloud.tools.jib.gradle.plugin:1.5.0 > gradle.plugin.com.google.cloud.tools:jib-gradle-plugin:1.5.0 > com.google.guava:guava:28.0-jre
                  > Could not resolve org.codehaus.mojo:animal-sniffer-annotations:1.17.
                     > Could not parse POM https://plugins.gradle.org/m2/org/codehaus/mojo/animal-sniffer-annotations/1.17/animal-sniffer-annotations-1.17.pom
                        > Could not resolve org.codehaus.mojo:animal-sniffer-parent:1.17.
                           > Could not resolve org.codehaus.mojo:animal-sniffer-parent:1.17.
                              > Could not get resource 'https://plugins.gradle.org/m2/org/codehaus/mojo/animal-sniffer-parent/1.17/animal-sniffer-parent-1.17.pom'.
                                 > Could not GET 'https://plugins.gradle.org/m2/org/codehaus/mojo/animal-sniffer-parent/1.17/animal-sniffer-parent-1.17.pom'.
                                    > Read timed out
               > Could not resolve io.grpc:grpc-context:1.19.0.
                 Required by:
                     project : > com.google.cloud.tools.jib:com.google.cloud.tools.jib.gradle.plugin:1.5.0 > gradle.plugin.com.google.cloud.tools:jib-gradle-plugin:1.5.0 > com.google.http-client:google-http-client:1.31.0 > io.opencensus:opencensus-api:0.21.0
                  > Skipped due to earlier error
            
            * Try:
            Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
            
            * Get more help at https://help.gradle.org
            
            BUILD FAILED in 1m 1s
            ERROR
            ERROR: build step 0 "gcr.io/cloud-builders/gradle" failed: exit status 1

[codecov]

Codecov Report

Merging #2865 into master will increase coverage by 0.04%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/resource/status.go	100% <100%> (ø)	⬆️
pkg/skaffold/deploy/resource/deployment.go	100% <100%> (ø)	⬆️

[balopat]

LGTM