JenkinsのGradle Wrapperでjavax.net.ssl.SSLHandshakeExceptionが出た場合の対処法

JenkinsでGradle Wrapperでのビルド時に以下のようなエラーが出た。
ググったところ、Javaのkeytoolで証明書やらなにやらやれとか出てきて色々やってみたが、結局JenkinsサーバのJavaをJava8にして、 Jenkinsの管理 ＞ システムの設定 のJDKもJava8にしたら解消した。

```java
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.
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[Gradle] - Launching build.
[foo] $ /var/lib/jenkins/workspace/foo/gradlew -DbranchName=bar clean build
Downloading https://services.gradle.org/distributions/gradle-2.4-bin.zip

Exception in thread "main" javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
	at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1884)
	at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:276)
	at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:270)
	at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1341)
	at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:153)
	at sun.security.ssl.Handshaker.processLoop(Handshaker.java:868)
	at sun.security.ssl.Handshaker.process_record(Handshaker.java:804)
	at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1016)
	at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1312)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1339)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1323)
	at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:563)
	at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185)
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1300)
	at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
	at org.gradle.wrapper.Download.downloadInternal(Download.java:58)
	at org.gradle.wrapper.Download.download(Download.java:44)
	at org.gradle.wrapper.Install$1.call(Install.java:59)
	at org.gradle.wrapper.Install$1.call(Install.java:46)
	at org.gradle.wrapper.ExclusiveFileAccessManager.access(ExclusiveFileAccessManager.java:65)
	at org.gradle.wrapper.Install.createDist(Install.java:46)
	at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:126)
	at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:61)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:385)
	at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
	at sun.security.validator.Validator.validate(Validator.java:260)
	at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:326)
	at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:231)
	at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:126)
	at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1323)
	... 19 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:196)
	at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:268)
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:380)
	... 25 more
Build step 'Invoke Gradle script' changed build result to FAILURE
Build step 'Invoke Gradle script' marked build as failure
Finished: FAILURE
```