Can't enter any toolbox containers

**Describe the bug**

I'm unable to `toolbox enter` any toolbox containers. After running `toolbox create` followed by `toolbox enter`, the command fails with:

```
Error: failed to initialize container fedora-toolbox-31
```

Looking at the logs for the failed toolbox container, I see:

```
level=debug msg="Running as real user ID 0"
level=debug msg="Resolved absolute path to the executable as /usr/bin/toolbox"
level=debug msg="TOOLBOX_PATH is /usr/bin/toolbox"
level=debug msg="XDG_RUNTIME_DIR is unset"
level=debug msg="XDG_RUNTIME_DIR set to /run/user/1000"
level=debug msg="Creating /run/.toolboxenv"
level=debug msg="Mounting tmpfs at /tmp"
level=debug msg="Monitoring host"
level=debug msg="Path /run/host/etc exists"
level=debug msg="Preparing to redirect /etc/host.conf to /run/host/etc/host.conf"
level=debug msg="/run/host/etc/host.conf isn't a symbolic link"
level=debug msg="Redirecting /etc/host.conf to /run/host/etc/host.conf"
level=debug msg="Preparing to redirect /etc/hosts to /run/host/etc/hosts"
level=debug msg="/run/host/etc/hosts isn't a symbolic link"
level=debug msg="Redirecting /etc/hosts to /run/host/etc/hosts"
level=debug msg="Preparing to redirect /etc/resolv.conf to /run/host/etc/resolv.conf"
level=debug msg="/run/host/etc/resolv.conf isn't a symbolic link"
level=debug msg="Redirecting /etc/resolv.conf to /run/host/etc/resolv.conf"
level=debug msg="Binding /etc/machine-id to /run/host/etc/machine-id"
level=debug msg="Creating /run/libvirt"
level=debug msg="Binding /run/libvirt to /run/host/run/libvirt"
level=debug msg="Creating /run/systemd/journal"
level=debug msg="Binding /run/systemd/journal to /run/host/run/systemd/journal"
level=debug msg="Creating /var/lib/flatpak"
level=debug msg="Binding /var/lib/flatpak to /run/host/var/lib/flatpak"
level=debug msg="Creating /var/log/journal"
level=debug msg="Binding /var/log/journal to /run/host/var/log/journal"
level=debug msg="Path /run/host/monitor exists"
level=debug msg="Preparing to redirect /etc/localtime to /run/host/monitor/localtime"
level=debug msg="/run/host/monitor/localtime isn't a symbolic link"
level=debug msg="Redirecting /etc/localtime to /run/host/monitor/localtime"
level=debug msg="Preparing to redirect /etc/timezone to /run/host/monitor/timezone"
level=debug msg="/run/host/monitor/timezone isn't a symbolic link"
level=debug msg="Redirecting /etc/timezone to /run/host/monitor/timezone"
level=debug msg="Looking up group for sudo"
level=debug msg="Group for sudo is wheel"
level=debug msg="Modifying user lars with UID 1000:"
level=debug msg=usermod
level=debug msg=--append
level=debug msg=--groups
level=debug msg=wheel
level=debug msg=--home
level=debug msg=/home/lars
level=debug msg=--shell
level=debug msg=/bin/bash
level=debug msg=--uid
level=debug msg=1000
level=debug msg=lars
usermod: failure while writing changes to /etc/passwd
Error: failed to modify user lars with UID 1000
```

**Output of `toolbox --version` (v0.0.90+)**

`toolbox version 0.0.95`

**Toolbox package info (`rpm -q toolbox`)**

(installed from source 40e7e6081e4be1604c0c1c4ebf2722d04b7900e5)

**Output of `podman version`**

```
Version: 2.1.0-dev
API Version: 1
Go Version: go1.13.11
Git Commit: 712d9f7cab967fda23547f49a01b44dfbbd13d57
Built: Fri Aug 3 20:00:00 2018
OS/Arch: linux/amd64
```

**Podman package info (`rpm -q podman`)**

`podman-2.1.0-1594142770.git54d16f3b.fc31.x86_64`

**Info about your OS**

Fedora 31