Support for multiple execution runtimes

[vladimirvivien]

Currently, crash-diagnostics uses a single execution runtime that assumes all commands are executed remotely using ssh or scp. While this assumption is easy to implement, it also makes the tool inflexible.

This issue is for the support of different executor runtimes. This would allow the tool to support commands with no prior assumptions where/how the command will be executed.

Runtimes

For instance, the followings shows several commands each using different runtimes.

FROM hosts:"host0.local host1.local"
CAPTURE cmd:"command -param0 -param1" runtime:"ssh"
COPY path:"/var/logs/log.txt" runtime:"http"
ENV JUMP="12.34.56.78"
RUN cmd:"ssh -i $HOME/.ssh/key_rsa -J user@$JUMP user@$FROM_HOST uptime" runtime:"shell" scope:"all"

runtime:ssh

• SSH protocol will be used for remote execution
• Each machine in FROM will be contacted on specified port (22 default)

runtime:http

• Assumes HTTP Get will be used to retrieve resource
• Each machine in FROM will be contacted on specified port (80 default)

runtime:shell

• A local shell is used to execute the command as it appears
• The local command will be executed for each machine in FROM
• Use scope to control how many time the command is executed

See #55 for command scopes