Pi should install the packages in an image with *any* name

[jordanmontt]

Currently, for installing a package the name "Pharo.image" is always taken look line:

pi/libexec/piGitHub.sh

Line 136 in 6964b46

./pharo --headless "$imageName" eval --save "$fullInstallExpr"

It is using the variable "Pharo.image"

pi/libexec/piEnvVars.sh

Line 23 in acb398c

imageName="Pharo.image"

It would be better to do a grep to find the file with an ".image" extension. This is useful for people that rename their images