add podman container|image exists

Add an exists subcommand to podman container and podman image that allows
users to verify the existence of a container or image by ID or name.  The return
code can be 0 (success), 1 (failed to find), or 125 (failed to work with runtime).

Issue #1845

Signed-off-by: baude <bbaude@redhat.com>

1 files changed, 40 insertions, 0 deletions

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+% PODMAN(1) Podman Man Pages
+% Brent Baude
+% November 2018
+# NAME
+podman-image-exists- Check if an image exists in local storage
+
+# SYNOPSIS
+**podman image exists**
+[**-h**|**--help**]
+IMAGE
+
+# DESCRIPTION
+**podman image exists** checks if an image exists in local storage. The **ID** or **Name**
+of the image may be used as input.  Podman will return an exit code
+of `0` when the image is found.  A `1` will be returned otherwise. An exit code of `125` indicates there
+was an issue accessing the local storage.
+
+## Examples ##
+
+Check if an image called `webclient` exists in local storage (the image does actually exist).
+```
+$ sudo podman image exists webclient
+$ echo $?
+0
+$
+```
+
+Check if an image called `webbackend` exists in local storage (the image does not actually exist).
+```
+$ sudo podman image exists webbackend
+$ echo $?
+1
+$
+```
+
+## SEE ALSO
+podman(1)
+
+# HISTORY
+November 2018, Originally compiled by Brent Baude (bbaude at redhat dot com)