docs: Remove "-ti" from docker invocations

The docker install guides end with a call to `docker run`. However, they
all specify `-ti` which is causing our CI to fail.

Remove the `-ti` so that the command works both under the CI and as
expected for the user.

Fixes kata-containers#175.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

Author: James O. D. Hunt

install/docker/centos-docker-install.md

@@ -47,7 +47,7 @@
    You are now ready to run Kata Containers:
 
    ```bash
-   $ sudo docker run -ti busybox uname -a
+   $ sudo docker run busybox uname -a
    ```
 
    The previous command shows details of the kernel version running inside the

install/docker/fedora-docker-install.md

@@ -48,7 +48,7 @@
    You are now ready to run Kata Containers:
 
    ```bash
-   $ sudo docker run -ti busybox uname -a
+   $ sudo docker run busybox uname -a
    ```
 
    The previous command shows details of the kernel version running inside the

install/docker/rhel-docker-install.md

@@ -48,7 +48,7 @@
    You are now ready to run Kata Containers:
 
    ```bash
-   $ sudo docker run -ti busybox uname -a
+   $ sudo docker run busybox uname -a
    ```
 
    The previous command shows details of the kernel version running inside the

install/docker/ubuntu-docker-install.md

@@ -51,7 +51,7 @@
    You are now ready to run Kata Containers:
 
    ```bash
-   $ sudo docker run -ti busybox uname -a
+   $ sudo docker run busybox uname -a
    ```
 
    The previous command shows details of the kernel version running inside the