In conda CI install yarp, icub-main and osqp-eigen from binaries on Linux/macOS and Windows

[traversaro]

Test PR that installs yarp and icub-main binaries from the experimental conda channel https://anaconda.org/robotology-staging/ (see robotology/robotology-superbuild#620 for some background). The channel is quite experimental and not ready for being used widely, but by starting to test it in a real scenario we can start understanding possible pitfalls.

[traversaro]

Linux/macOS are working fine, while Windows is failing with:

2021-02-16T08:24:20.3326611Z -- Could NOT find Doxygen (missing: DOXYGEN_EXECUTABLE) 
2021-02-16T08:24:20.3345240Z -- Configuring done
2021-02-16T08:24:20.7676046Z CMake Error at src/solid-shapes/CMakeLists.txt:6 (add_library):
2021-02-16T08:24:20.7677777Z   Target "idyntree-solid-shapes" links to target "assimp::assimp" but the
2021-02-16T08:24:20.7678721Z   target was not found.  Perhaps a find_package() call is missing for an
2021-02-16T08:24:20.7679687Z   IMPORTED target, or an ALIAS target is missing?
2021-02-16T08:24:20.7682667Z 
2021-02-16T08:24:20.7683131Z 
2021-02-16T08:24:20.7683773Z CMake Error at src/solid-shapes/CMakeLists.txt:6 (add_library):
2021-02-16T08:24:20.7685135Z   Target "idyntree-solid-shapes" links to target "assimp::assimp" but the
2021-02-16T08:24:20.7686475Z   target was not found.  Perhaps a find_package() call is missing for an
2021-02-16T08:24:20.7687363Z   IMPORTED target, or an ALIAS target is missing?
2021-02-16T08:24:20.7688280Z 
2021-02-16T08:24:20.7689093Z 
2021-02-16T08:24:20.7690011Z CMake Error at src/solid-shapes/CMakeLists.txt:6 (add_library):
2021-02-16T08:24:20.7691181Z   Target "idyntree-solid-shapes" links to target "assimp::assimp" but the
2021-02-16T08:24:20.7692677Z   target was not found.  Perhaps a find_package() call is missing for an
2021-02-16T08:24:20.7693434Z   IMPORTED target, or an ALIAS target is missing?
2021-02-16T08:24:20.7693910Z 
2021-02-16T08:24:20.7694231Z 
2021-02-16T08:24:20.7695047Z CMake Error at src/solid-shapes/CMakeLists.txt:6 (add_library):
2021-02-16T08:24:20.7696201Z   Target "idyntree-solid-shapes" links to target "assimp::assimp" but the
2021-02-16T08:24:20.7697603Z   target was not found.  Perhaps a find_package() call is missing for an
2021-02-16T08:24:20.7699303Z   IMPORTED target, or an ALIAS target is missing?
2021-02-16T08:24:20.7700256Z 
2021-02-16T08:24:20.7700977Z 

that is a strange message as the idyntree-solid-shapes should have been compiled and linked to assimp::assimp even before this PR, but probably there is some CMake config cross talking or similar, it needs to be checked out.

[traversaro]

The problem was that if YARP is enabled, find_package(YCM) is transitively called by find_package(YARP), and the Findassimp.cmake module of YCM is added to the CMAKE_MODULE_PATH. Unfortunately the Findassimp.cmake script of YCM is broken as described in robotology/ycm-cmake-modules#371 . To avoid requiring to wait for the fix to get in YCM and a YCM release do be made, in this PR we just call find_package(assimp NO_MODULE), so Findassimp.cmake is ignored even if is present in the CMAKE_MODULE_PATH.

[traversaro]

The PR is now ready for review.