Push to Docker registry hosted on Subpath

**Environment**:

- *Jib version:* 2.2.0
- *Build tool:* Maven
- *OS:* MacOs

**Description of the issue**:
Docker registry is hosted on subpath at example.com/myRegistry. So, the image would be example.com/myRegistry/myDockerImage. Jib seems to take example.com as the image registry URL.

**Expected behavior**:
example.com/myRegistry to be taken as image URL.

**Steps to reproduce**:

1. set `to.image` to example.com/myRegistry/myDockerImage

**Log output**:
[INFO] Containerizing application to plms.tgrc.tesco.org/registry/configserver...
[WARNING] Base image 'azul/zulu-openjdk:8u232' does not use a specific image digest - build may not be reproducible
[INFO] Using credentials from for plms.tgrc.tesco.org/registry/configserver
[WARNING] Cannot verify server at https://plms.tgrc.tesco.org/v2/. Attempting again with no TLS verification.
[INFO] The base image requires auth. Trying again for azul/zulu-openjdk:8u232...
[INFO] Executing tasks:
[INFO] [====== ] 18.5% complete
[INFO] > pulling base image manifest
[INFO] > building dependencies layer
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.436 s
[INFO] Finished at: 2020-05-14T20:27:13+05:30
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.google.cloud.tools:jib-maven-plugin:2.2.0:build (default-cli) on project config-server: Tried to retrieve authentication method for plms.tgrc.tesco.org but failed because: registry returned error code 404; possible causes include invalid or wrong reference. Actual error output follows:
[ERROR] default backend - 404
[ERROR] | If this is a bug, please file an issue at https://github.com/GoogleContainerTools/jib/issues/new: 404 Not Found
[ERROR] default backend - 404
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException